01 - Preheat the oven to 400°F. Line a baking tray with parchment paper.
02 - Spread the butternut squash cubes on the tray, drizzle with 1 teaspoon olive oil, season with salt and pepper, then roast for 25 minutes until tender and lightly browned.
03 - Meanwhile, cook the macaroni in salted boiling water following package instructions until al dente. Drain and set aside.
04 - Melt butter in a large saucepan over medium heat. Add chopped onion and minced garlic, cooking until softened, about 3 to 4 minutes.
05 - Stir in flour and cook for 1 minute. Gradually whisk in milk, stirring constantly until the sauce thickens, approximately 5 minutes.
06 - Add the roasted butternut squash to the sauce and blend with an immersion blender until smooth.
07 - Stir in grated cheddar, Parmesan, nutmeg, mustard powder, salt, and black pepper. Remove from heat once cheese is melted and sauce is smooth.
08 - Mix the sauce thoroughly with the drained macaroni, then transfer to a lightly greased baking dish.
09 - In a small bowl, toss panko breadcrumbs with 2 teaspoons olive oil and grated Parmesan cheese. Sprinkle evenly over the pasta.
10 - Bake for 15 minutes or until the topping is golden and the dish is bubbling. Allow to stand for 5 minutes before serving.